Something I wrote elsewhere.
Lets start with wheels.
If you don’t understand what offset is, use Google. However, what size wheels fit an MX-5?
Tyre width and “Lows” make a difference. Assuming you are going to fit proper size tyres then for a MK1, from the hub face of the car, the bit the wheel actually bolts to, the original 14" MK1 wheel’s outer face was about 35mm further out. So if you want wider wheels, you need to work out your width and offset.
So if you have a 15 x 7J wheel with a 30 offset, will it fit?
Width in inches so 7" x 25.4 to give the wheel width (they are wider than this, but this is good enough) 177.8 (you can round it up to 178.
Divide that by 2 to give you half the width and then take away the offset 178/2 - 30 = 59mm.
So here are the important figures.
For MK1 cars, if that final figure is below 66, for normal tyres and suspension you will require no body mods to fit the wheels.
For MK2 cars the figure is 78
If you go above these figures you are likely to need to roll your arches. Spastic camber is not a solution and it will cost you more in tyres that the cost of rolling.
If you fit big tyres the situation will be different, so 225 50 15 tyres would require the arches rolling and pulling if you are at the 78 figure for instance.